Novel approaches for simulating hot forming and heat treatment

© Fraunhofer IWM

Using novel approaches, we enable the detailed simulation of material behavior of metallic materials in hot forming and heat treatment. Our approach links thermo-mechanical material behavior and microstructure evolution using a comprehensive thermodynamic approach. This allows us to efficiently model viscoplasticity, recovery, recrystallization, grain coarsening, texture evolution, and precipitation, as well as the associated strengthening and softening processes. Despite the complexity of the material model, parameter determination requires limited effort because most parameters have clear physical meaning.

The material model is implemented as a program for process simulation, which can be used to predict thermo-mechanical material behavior and microstructure evolution. Besides its application for thermo-mechanically coupled simulations, it can be used for post-processing of forming simulations with commercial finite element simulations. The program can be applied to hot and cold forming processes, heat treatment and any combination of these processes. This allows us to model an entire process chain without having to transfer data from one model to another between the steps. Typical applications are the design, evaluation, and optimization of process routes. Furthermore, applications in process control are conceivable.

Application: Hot forming of microalloyed steel

The material model was calibrated using compression tests of a microalloyed steel at different temperatures and strain rates. The model parameters were determined using the stress-strain curves and the grain size distributions before and after forming determined in metallographic analyses. Due to the use of niobium as a microalloying element, dynamic recrystallization is retarded by solute drag and the pinning effect of NbC precipitates, which can be specifically exploited during hot forming.

© Fraunhofer IWM
Stress-strain diagrams (simulation and experiment) and evolution of the mean grain size (simulation).
© Fraunhofer IWM
Calculated grain size distributions before and after forming at various temperatures and strain rates.

Microstructure evolution of aluminum alloys during extrusion

In collaboration with the Institute of Forming Technology and Lightweight Components (IUL) at TU Dortmund University, we are working on an Industrial Collective Research (IGF) project on microstructure evolution modeling for extrusion processes. The objective is to develop a practical approach for predicting the grain structure evolving during extrusion processes by means of numerical simulations. For application, the goal is to provide a calculation tool to estimate the microstructure quality of extruded products in order to enable faster adaptation of the processing conditions to new materials or changed process parameters. In the research project, we calibrate our material model using experiments. Next, we will make use of the model to simulate a large number of different thermo-mechanical tests. Considering the results from these virtual tests, the experimental database will be considerably expanded. Finally, based on the expanded database, we will calibrate a physically motivated and numerically very efficient material model. The efficient model will be implemented as a material routine for commercial finite element software. We will thus provide a fast and efficient tool to predict the development of the grain structure during extrusion of aluminum profiles.

Video: Hot compression test in the »Gleeble 3150« thermo-mechanical simulator.

Grain coarsening and precipitation in copper alloys

In precipitate-forming copper alloys such as CuNiSi alloys, a high strength can be reached. Furthermore, the microstructural stability at elevated temperatures can be significantly enhanced. Using our material model, the dependence of the material properties on process parameters such as temperature, time and degree of forming can be predicted.

© Fraunhofer IWM
Grain coarsening in copper: In precipitate containing alloys, coarsening is significantly retarded.
© Fraunhofer IWM
Evolution of microstructure and strength during artificial aging of a copper alloy dependent on cold deformation and aging time.

Publications

 

  • Hebbar, S.; Kertsch, L.; Butz, A., Optimizing heat treatment parameters for the W-temper forming of 7xxx series aluminum alloys, Metals 10/10 (2020) Art. 1361, 15 Seiten Link
  • Diehl, M.; Kertsch, L.; Traka, K.; Helm, D.; Raabe, D., Site-specific quasi in situ investigation of primary static recrystallization in a low carbon steel, Materials Science and Engineering: A 755 (2019) 295-306 Link
  • Kertsch, L.; Helm, D., A thermodynamically consistent model for elastoplasticity, recovery, recrystallization and grain coarsening, International Journal of Solids and Structures 152-153 (2018) 185-195 Link
  • Kertsch, L.; Helm, D.; Modelling grain growth in the framework of rational extended thermodynamics; Modelling and Simulation in Materials Science and Engineering MSMSE 24/4 (2016) 45001-45017 Link

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